The invention relates to an optical monitoring means.
For monitoring danger areas around machines, security areas, elevator doors or the safety monitoring of apartments photoelectric detectors and beam arrays using same have so far been employed. Such beam arrays suffer from the disadvantage that a plurality of active elements, i. e. light sources and sensors, must be arranged on either side of the monitored area, something which increases the costs of such a beam array. Furthermore all active elements must be connected together by wiring in order to permit synchronization and signal processing. The electronic circuitry necessary for this is also a substantial cost factor.
The German patent publication 38 42 142 C1 discloses a method for the optical recognition of objects, the means comprising a sensor means, on which an objective projects the image of a pattern field, and a signal processing means in order to ascertain whether the image received by the sensor means possesses the same optical characteristics as the pattern field. At one end of the monitored area there is therefore a passive element, namely the pattern field, whereas the sensor means together with the associated objective is placed at the other end of the monitored area so that no power supply and control lines must be laid from the one end of the monitored area to the other end. Furthermore the number of active elements is reduced.